Well, by definition (I think) Arrangers are keyboards that play styles--real-time backgrounds that let you "arrange" songs on the fly. If a synth or workstation plays styles, it is also an arranger.
Clavinovas are arrangers in big cabinets.
A lot of the distinction is just the terminology used.
You can, of course, use an arranger module such as Roland BK7 or Ketron Audya 5 or Midjay, and control them with any midi-capable keyboard.